Fastening members having a thread structure such as bolts and nuts are widely used in the related art. In order to enable a bolt to be actually tightened into a nut, it is necessary to provide a dimensional tolerance between the outside diameter and the effective diameter of the bolt and the inside diameter and the effective diameter of the nut. Meanwhile, such a tolerance may loosen the bolt and the nut. Various contrivances have been made in the related art to prevent occurrence of such loosening.
Japanese Utility Model Application Publication No. JP-U-Sho 53-88664 and Japanese Patent Application Publication No. JP-A-Hei 8-177839 disclose a male thread structure partially including a screw thread provided with a pressure flank surface, the flank angle of which is smaller than the flank angle of a basic profile, and a clearance flank surface, the flank angle of which is larger than the flank angle of the basic profile.
Japanese Patent Application Publication No. JP-A-Hei 11-51033 discloses a fastening member including a slit formed in the crest of a screw thread and extending in a direction that is perpendicular to the axis of the thread, and a widely formed root.
A method of preventing loosening by forming a resin coating layer on part of a screw thread is also proposed.
Japanese Patent Application Publication No. JP-A-2006-57801 discloses a firmly tightening screw as a related art of the present invention.